Compounds having knockdown and lethal efficacy against medically important insects such as mosquitoes and flies and having excellent safety to human and animals include pyrethrin contained in a flower of Chrysanthemum cinerariifolium and pyrethroid compounds whose chemical structure is similar to that of pyrethrin.
However, although the development of resistance to natural pyrethrin in the medically important insects is very slight, the development of resistance to synthetic pyrethroid compounds increases recently, and a countermeasure thereto is urgent requirement.
In the pyrethroid compounds, the research and development of compounds which also show insecticidal efficacy against the resistant noxious insects are furthered in each country reflecting such a situation. As a result, a dangerous compound which exerts undesired influence to human and animals has come to appear.
Growing Chrysanthemum cinerariifolium takes two years from seeding to bloom and harvesting, and cannot rely only on nature.
Discovery of new insecticidal compounds and insecticidal ingredients using these compounds has been sought in view of such a situation of pyrethrin and synthesized pyrethroid compounds.
Marigold which is an annual herb of Compositae Tagetes native to Mexico and has a petal of an orange or yellow color is cultivated as an ornamental plant.
It is also known that its roots, flower parts, and leaves have bactericidal, nematicidal, fungicidal, insecticidal, and insect repellent effects.
However, these effects are very slight, and the chemical structure of the active ingredient is unknown. Therefore, they are not yet practically used.
Note that, the researches on the components having weak insecticidal efficacy contained in the flower parts and leaves of marigold as described above have been reported one by one since around 1975, in which although the existence of various substances has been discussed, it is only a guess altogether and chemical analysis has not been conducted at all.
For example, Khanna et al. of India announced in 1975, as shown in Non Patent Literature 1, that the insecticidal ingredient of marigold was the same as the insecticidal ingredient contained in the flower of Chrysanthemum cinerariifolium, pyrethrin, and includes 6 chemical components.
However, as shown in Non Patent Literature 2, Wells et al. of United States of America reported in 1993 the existence of 11 compounds from an extract matter of the flower of marigold, and reported that the insecticidal ingredient was not pyrethrin but would be a thiophene group including 1 sulfur (S) and 4 carbons (C).
With respect to the search of chemical substances contained in marigold, Bohlmann et al. of the Federal Republic of West Germany studied in 1978, as shown in Non Patent Literature 3, the compounds contained in marigold and announced the existence of 22 compounds. In the literature, they have reported the existence of a ketone which contain no sulfur other than the thiophene group. The compound B in the present application to be described below is also included (in Non Patent Literature 3, the compound is named “Bis-trans-ocimenon”.).
Note that, the paper aims at searching chemical substances contained in marigold and does not refer to bioactive action thereof at all.
However, no work including conducting minute experiments on chemical substances in marigold and then identifying, by the experiments, a compound which exhibits extraordinary insecticidal efficacy compared with conventional insecticides such as pyrethroid compounds has been conducted.